From 52f09a7bd1fef68a12dae1ee0e22f9d205c966e0 Mon Sep 17 00:00:00 2001
From: sjplimp <sjplimp@f3b2605a-c512-4ea7-a41b-209d697bcdaa>
Date: Thu, 7 Mar 2013 20:46:54 +0000
Subject: [PATCH] git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@9611
 f3b2605a-c512-4ea7-a41b-209d697bcdaa

---
 src/MOLECULE/Install.sh                |   4 +
 src/MOLECULE/pair_lj_cut_tip4p_cut.cpp | 669 +++++++++++++++++++++++++
 src/MOLECULE/pair_lj_cut_tip4p_cut.h   |  66 +++
 3 files changed, 739 insertions(+)
 create mode 100644 src/MOLECULE/pair_lj_cut_tip4p_cut.cpp
 create mode 100644 src/MOLECULE/pair_lj_cut_tip4p_cut.h

diff --git a/src/MOLECULE/Install.sh b/src/MOLECULE/Install.sh
index 58deb45525..5a30b0e86b 100644
--- a/src/MOLECULE/Install.sh
+++ b/src/MOLECULE/Install.sh
@@ -35,6 +35,7 @@ if (test $1 = 1) then
   cp pair_hbond_dreiding_morse.cpp ..
   cp pair_lj_charmm_coul_charmm.cpp ..
   cp pair_lj_charmm_coul_charmm_implicit.cpp ..
+  cp pair_lj_cut_tip4p_cut.cpp ..
 
   cp angle_charmm.h ..
   cp angle_cosine.h ..
@@ -69,6 +70,7 @@ if (test $1 = 1) then
   cp pair_hbond_dreiding_morse.h ..
   cp pair_lj_charmm_coul_charmm.h ..
   cp pair_lj_charmm_coul_charmm_implicit.h ..
+  cp pair_lj_cut_tip4p_cut.h ..
 
 elif (test $1 = 0) then
 
@@ -105,6 +107,7 @@ elif (test $1 = 0) then
   rm -f ../pair_hbond_dreiding_morse.cpp
   rm -f ../pair_lj_charmm_coul_charmm.cpp
   rm -f ../pair_lj_charmm_coul_charmm_implicit.cpp
+  rm -f ../pair_lj_cut_tip4p_cut.cpp
 
   rm -f ../angle_charmm.h
   rm -f ../angle_cosine.h
@@ -139,5 +142,6 @@ elif (test $1 = 0) then
   rm -f ../pair_hbond_dreiding_morse.h
   rm -f ../pair_lj_charmm_coul_charmm.h
   rm -f ../pair_lj_charmm_coul_charmm_implicit.h
+  rm -f ../pair_lj_cut_tip4p_cut.h
 
 fi
diff --git a/src/MOLECULE/pair_lj_cut_tip4p_cut.cpp b/src/MOLECULE/pair_lj_cut_tip4p_cut.cpp
new file mode 100644
index 0000000000..4bd52d293e
--- /dev/null
+++ b/src/MOLECULE/pair_lj_cut_tip4p_cut.cpp
@@ -0,0 +1,669 @@
+/* ----------------------------------------------------------------------
+   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
+   http://lammps.sandia.gov, Sandia National Laboratories
+   Steve Plimpton, sjplimp@sandia.gov
+
+   Copyright (2003) Sandia Corporation.  Under the terms of Contract
+   DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
+   certain rights in this software.  This software is distributed under
+   the GNU General Public License.
+
+   See the README file in the top-level LAMMPS directory.
+------------------------------------------------------------------------- */
+
+/* ----------------------------------------------------------------------
+   Contributing author: Pavel Elkind (Gothenburg University)
+------------------------------------------------------------------------- */
+
+#include "math.h"
+#include "stdlib.h"
+#include "pair_lj_cut_tip4p_cut.h"
+#include "atom.h"
+#include "force.h"
+#include "neighbor.h"
+#include "neigh_list.h"
+#include "domain.h"
+#include "angle.h"
+#include "bond.h"
+#include "comm.h"
+#include "memory.h"
+#include "error.h"
+
+using namespace LAMMPS_NS; 
+
+/* ---------------------------------------------------------------------- */
+
+PairLJCutTIP4PCut::PairLJCutTIP4PCut(LAMMPS *lmp) : Pair(lmp)
+{
+  single_enable = 0;
+
+  nmax = 0;
+  hneigh = NULL;
+  newsite = NULL;
+
+  // TIP4P cannot compute virial as F dot r
+  // due to finding bonded H atoms which are not near O atom
+
+  no_virial_fdotr_compute = 1;
+}
+
+/* ---------------------------------------------------------------------- */
+
+PairLJCutTIP4PCut::~PairLJCutTIP4PCut()
+{
+  if (allocated) {
+    memory->destroy(setflag);
+    memory->destroy(cutsq);
+
+    memory->destroy(cut_lj);
+    memory->destroy(cut_ljsq);
+    memory->destroy(epsilon);
+    memory->destroy(sigma);
+    memory->destroy(lj1);
+    memory->destroy(lj2);
+    memory->destroy(lj3);
+    memory->destroy(lj4);
+    memory->destroy(offset);
+  }
+
+  memory->destroy(hneigh);
+  memory->destroy(newsite);
+}
+
+/* ---------------------------------------------------------------------- */
+
+void PairLJCutTIP4PCut::compute(int eflag, int vflag)
+{
+  int i,j,ii,jj,inum,jnum,itype,jtype;
+  double qtmp,xtmp,ytmp,ztmp,delx,dely,delz,evdwl,ecoul;
+  double rsq,r2inv,r6inv,forcecoul,forcelj,factor_lj,factor_coul;
+  int *ilist,*jlist,*numneigh,**firstneigh;
+
+  int key;
+  int n,vlist[6];
+  int iH1,iH2,jH1,jH2;
+  double cforce;
+  double fO[3],fH[3],fd[3],v[6],xH1[3],xH2[3];
+  double *x1,*x2;
+
+  evdwl = ecoul = 0.0;
+  if (eflag || vflag) ev_setup(eflag,vflag);
+  else evflag = vflag_fdotr = 0;
+
+  // reallocate hneigh & newsite if necessary
+  // initialize hneigh[0] to -1 on steps when reneighboring occurred
+  // initialize hneigh[2] to 0 every step
+
+  int nlocal = atom->nlocal;
+  int nall = nlocal + atom->nghost;
+
+  if (atom->nmax > nmax) {
+    nmax = atom->nmax;
+    memory->destroy(hneigh);
+    memory->create(hneigh,nmax,3,"pair:hneigh");
+    memory->destroy(newsite);
+    memory->create(newsite,nmax,3,"pair:newsite");
+  }
+  if (neighbor->ago == 0)
+    for (i = 0; i < nall; i++) hneigh[i][0] = -1;
+  for (i = 0; i < nall; i++) hneigh[i][2] = 0;
+
+  double **f = atom->f;
+  double **x = atom->x;
+  double *q = atom->q;
+  int *type = atom->type;
+  double *special_lj = force->special_lj;
+  double *special_coul = force->special_coul;
+  int newton_pair = force->newton_pair;
+  double qqrd2e = force->qqrd2e;
+
+  inum = list->inum;
+  ilist = list->ilist;
+  numneigh = list->numneigh;
+  firstneigh = list->firstneigh;
+
+  // loop over neighbors of my atoms
+
+  for (ii = 0; ii < inum; ii++) {
+    i = ilist[ii];
+    qtmp = q[i];
+    xtmp = x[i][0];
+    ytmp = x[i][1];
+    ztmp = x[i][2];
+    itype = type[i];
+
+    if (itype == typeO) {
+      if (hneigh[i][0] < 0) {
+        hneigh[i][0] = iH1 = atom->map(atom->tag[i] + 1);
+        hneigh[i][1] = iH2 = atom->map(atom->tag[i] + 2);
+        hneigh[i][2] = 1;
+        if (iH1 == -1 || iH2 == -1)
+          error->one(FLERR,"TIP4P hydrogen is missing");
+        if (atom->type[iH1] != typeH || atom->type[iH2] != typeH)
+          error->one(FLERR,"TIP4P hydrogen has incorrect atom type");
+        compute_newsite(x[i],x[iH1],x[iH2],newsite[i]);
+      } else {
+        iH1 = hneigh[i][0];
+        iH2 = hneigh[i][1];
+        if (hneigh[i][2] == 0) {
+          hneigh[i][2] = 1;
+          compute_newsite(x[i],x[iH1],x[iH2],newsite[i]);
+        }
+      }
+      x1 = newsite[i];
+    } else x1 = x[i];
+
+    jlist = firstneigh[i];
+    jnum = numneigh[i];
+
+    for (jj = 0; jj < jnum; jj++) {
+      j = jlist[jj];
+      factor_lj = special_lj[sbmask(j)];
+      factor_coul = special_coul[sbmask(j)];
+      j &= NEIGHMASK;
+
+      delx = xtmp - x[j][0];
+      dely = ytmp - x[j][1];
+      delz = ztmp - x[j][2];
+      rsq = delx*delx + dely*dely + delz*delz;
+      jtype = type[j];
+
+      // LJ interaction based on true rsq
+
+      if (rsq < cut_ljsq[itype][jtype]) {
+        r2inv = 1.0/rsq;
+        r6inv = r2inv*r2inv*r2inv;
+        forcelj = r6inv * (lj1[itype][jtype]*r6inv - lj2[itype][jtype]);
+        forcelj *= factor_lj * r2inv;
+
+        f[i][0] += delx*forcelj;
+        f[i][1] += dely*forcelj;
+        f[i][2] += delz*forcelj;
+        f[j][0] -= delx*forcelj;
+        f[j][1] -= dely*forcelj;
+        f[j][2] -= delz*forcelj;
+
+        if (eflag) {
+          evdwl = r6inv*(lj3[itype][jtype]*r6inv-lj4[itype][jtype]) -
+            offset[itype][jtype];
+          evdwl *= factor_lj;
+        } else evdwl = 0.0;
+
+        if (evflag) ev_tally(i,j,nlocal,newton_pair,
+                             evdwl,0.0,forcelj,delx,dely,delz);
+      }
+
+      // adjust rsq and delxyz for off-site O charge(s) if necessary
+      // but only if they are within reach
+
+      if (rsq < cut_coulsqplus) {
+        if (itype == typeO || jtype == typeO) {
+
+          // if atom J = water O, set x2 = offset charge site
+          // else x2 = x of atom J
+
+          if (jtype == typeO) {
+            if (hneigh[j][0] < 0) {
+              hneigh[j][0] = jH1 = atom->map(atom->tag[j] + 1);
+              hneigh[j][1] = jH2 = atom->map(atom->tag[j] + 2);
+              hneigh[j][2] = 1;
+              if (jH1 == -1 || jH2 == -1)
+                error->one(FLERR,"TIP4P hydrogen is missing");
+              if (atom->type[jH1] != typeH || atom->type[jH2] != typeH)
+                error->one(FLERR,"TIP4P hydrogen has incorrect atom type");
+              compute_newsite(x[j],x[jH1],x[jH2],newsite[j]);
+            } else {
+              jH1 = hneigh[j][0];
+              jH2 = hneigh[j][1];
+              if (hneigh[j][2] == 0) {
+                hneigh[j][2] = 1;
+                compute_newsite(x[j],x[jH1],x[jH2],newsite[j]);
+              }
+            }
+            x2 = newsite[j];
+          } else x2 = x[j];
+
+          delx = x1[0] - x2[0];
+          dely = x1[1] - x2[1];
+          delz = x1[2] - x2[2];
+          rsq = delx*delx + dely*dely + delz*delz;
+        }
+
+        // Coulombic interaction based on modified rsq
+
+        if (rsq < cut_coulsq) {
+          r2inv = 1.0 / rsq;
+          forcecoul = qqrd2e * qtmp * q[j] * sqrt(r2inv);
+          cforce = factor_coul * forcecoul * r2inv;
+
+        // if i,j are not O atoms, force is applied directly;
+        // if i or j are O atoms, force is on fictitious atom & partitioned
+        // force partitioning due to Feenstra, J Comp Chem, 20, 786 (1999)
+        // f_f = fictitious force, fO = f_f (1 - 2 alpha), fH = alpha f_f
+        // preserves total force and torque on water molecule
+        // virial = sum(r x F) where each water's atoms are near xi and xj
+        // vlist stores 2,4,6 atoms whose forces contribute to virial
+
+          n = 0;
+          key = 0;
+
+          if (itype != typeO) {
+            f[i][0] += delx * cforce;
+            f[i][1] += dely * cforce;
+            f[i][2] += delz * cforce;
+
+            if (vflag) {
+              v[0] = x[i][0] * delx * cforce;
+              v[1] = x[i][1] * dely * cforce;
+              v[2] = x[i][2] * delz * cforce;
+              v[3] = x[i][0] * dely * cforce;
+              v[4] = x[i][0] * delz * cforce;
+              v[5] = x[i][1] * delz * cforce;
+            }
+            vlist[n++] = i;
+
+          } else {
+            key++;
+
+            fd[0] = delx*cforce;
+            fd[1] = dely*cforce;
+            fd[2] = delz*cforce;
+
+            fO[0] = fd[0]*(1.0 - alpha);
+            fO[1] = fd[1]*(1.0 - alpha);
+            fO[2] = fd[2]*(1.0 - alpha);
+
+            fH[0] = 0.5 * alpha * fd[0];
+            fH[1] = 0.5 * alpha * fd[1];
+            fH[2] = 0.5 * alpha * fd[2];
+
+            f[i][0] += fO[0];
+            f[i][1] += fO[1];
+            f[i][2] += fO[2];
+
+            f[iH1][0] += fH[0];
+            f[iH1][1] += fH[1];
+            f[iH1][2] += fH[2];
+
+            f[iH2][0] += fH[0];
+            f[iH2][1] += fH[1];
+            f[iH2][2] += fH[2];
+
+            if(vflag) {
+              domain->closest_image(x[i],x[iH1],xH1);
+              domain->closest_image(x[i],x[iH2],xH2);
+
+              v[0] = x[i][0]*fO[0] + xH1[0]*fH[0] + xH2[0]*fH[0];
+              v[1] = x[i][1]*fO[1] + xH1[1]*fH[1] + xH2[1]*fH[1];
+              v[2] = x[i][2]*fO[2] + xH1[2]*fH[2] + xH2[2]*fH[2];
+              v[3] = x[i][0]*fO[1] + xH1[0]*fH[1] + xH2[0]*fH[1];
+              v[4] = x[i][0]*fO[2] + xH1[0]*fH[2] + xH2[0]*fH[2];
+              v[5] = x[i][1]*fO[2] + xH1[1]*fH[2] + xH2[1]*fH[2];
+            }
+            vlist[n++] = i;
+            vlist[n++] = iH1;
+            vlist[n++] = iH2;
+          }
+
+          if (jtype != typeO) {
+            f[j][0] -= delx * cforce;
+            f[j][1] -= dely * cforce;
+            f[j][2] -= delz * cforce;
+
+            if (vflag) {
+              v[0] -= x[j][0] * delx * cforce;
+              v[1] -= x[j][1] * dely * cforce;
+              v[2] -= x[j][2] * delz * cforce;
+              v[3] -= x[j][0] * dely * cforce;
+              v[4] -= x[j][0] * delz * cforce;
+              v[5] -= x[j][1] * delz * cforce;
+            }
+            vlist[n++] = j;
+
+          } else {
+            key += 2;
+
+            fd[0] = -delx*cforce;
+            fd[1] = -dely*cforce;
+            fd[2] = -delz*cforce;
+
+            fO[0] = fd[0]*(1 - alpha);
+            fO[1] = fd[1]*(1 - alpha);
+            fO[2] = fd[2]*(1 - alpha);
+
+            fH[0] = 0.5 * alpha * fd[0];
+            fH[1] = 0.5 * alpha * fd[1];
+            fH[2] = 0.5 * alpha * fd[2];
+
+            f[j][0] += fO[0];
+            f[j][1] += fO[1];
+            f[j][2] += fO[2];
+
+            f[jH1][0] += fH[0];
+            f[jH1][1] += fH[1];
+            f[jH1][2] += fH[2];
+
+            f[jH2][0] += fH[0];
+            f[jH2][1] += fH[1];
+            f[jH2][2] += fH[2];
+
+            if (vflag) {
+              domain->closest_image(x[j],x[jH1],xH1);
+              domain->closest_image(x[j],x[jH2],xH2);
+
+              v[0] += x[j][0]*fO[0] + xH1[0]*fH[0] + xH2[0]*fH[0];
+              v[1] += x[j][1]*fO[1] + xH1[1]*fH[1] + xH2[1]*fH[1];
+              v[2] += x[j][2]*fO[2] + xH1[2]*fH[2] + xH2[2]*fH[2];
+              v[3] += x[j][0]*fO[1] + xH1[0]*fH[1] + xH2[0]*fH[1];
+              v[4] += x[j][0]*fO[2] + xH1[0]*fH[2] + xH2[0]*fH[2];
+              v[5] += x[j][1]*fO[2] + xH1[1]*fH[2] + xH2[1]*fH[2];
+            }
+            vlist[n++] = j;
+            vlist[n++] = jH1;
+            vlist[n++] = jH2;
+          }
+
+          if (eflag) {
+            ecoul = qqrd2e * qtmp * q[j] * sqrt(r2inv);
+            ecoul *= factor_coul;
+          } else ecoul = 0.0;
+
+          if (evflag) ev_tally_tip4p(key,vlist,v,ecoul,alpha);
+        }
+      }
+    }
+  }
+}
+
+/* ----------------------------------------------------------------------
+   allocate all arrays
+------------------------------------------------------------------------- */
+
+void PairLJCutTIP4PCut::allocate()
+{
+  allocated = 1;
+  int n = atom->ntypes;
+
+  memory->create(setflag,n+1,n+1,"pair:setflag");
+  for (int i = 1; i <= n; i++)
+    for (int j = i; j <= n; j++)
+      setflag[i][j] = 0;
+
+  memory->create(cutsq,n+1,n+1,"pair:cutsq");
+
+  memory->create(cut_lj,n+1,n+1,"pair:cut_lj");
+  memory->create(cut_ljsq,n+1,n+1,"pair:cut_ljsq");
+  memory->create(epsilon,n+1,n+1,"pair:epsilon");
+  memory->create(sigma,n+1,n+1,"pair:sigma");
+  memory->create(lj1,n+1,n+1,"pair:lj1");
+  memory->create(lj2,n+1,n+1,"pair:lj2");
+  memory->create(lj3,n+1,n+1,"pair:lj3");
+  memory->create(lj4,n+1,n+1,"pair:lj4");
+  memory->create(offset,n+1,n+1,"pair:offset");
+}
+
+/* ----------------------------------------------------------------------
+   global settings
+------------------------------------------------------------------------- */
+
+void PairLJCutTIP4PCut::settings(int narg, char **arg)
+{
+  if (narg != 7) error->all(FLERR,"Illegal pair_style command");
+
+  typeO = force->inumeric(arg[0]);
+  typeH = force->inumeric(arg[1]);
+  typeB = force->inumeric(arg[2]);
+  typeA = force->inumeric(arg[3]);
+  qdist = force->numeric(arg[4]);
+
+  cut_lj_global = force->numeric(arg[5]);
+  cut_coul = force->numeric(arg[6]);
+  cut_coulsq = cut_coul * cut_coul;
+  cut_coulsqplus = (cut_coul + 2.0*qdist) * (cut_coul + 2.0*qdist);
+
+  if (allocated) {
+    int i,j;
+    for (i = 1; i <= atom->ntypes; i++)
+      for (j = i+1; j <= atom->ntypes; j++)
+        if (setflag[i][j]) cut_lj[i][j] = cut_lj_global;
+  }
+}
+
+/* ----------------------------------------------------------------------
+   set coeffs for one or more type pairs
+------------------------------------------------------------------------- */
+
+void PairLJCutTIP4PCut::coeff(int narg, char **arg)
+{
+  if (narg != 4) error->all(FLERR,"Incorrect args for pair coefficients");
+  if (!allocated) allocate();
+
+  int ilo,ihi,jlo,jhi;
+  force->bounds(arg[0],atom->ntypes,ilo,ihi);
+  force->bounds(arg[1],atom->ntypes,jlo,jhi);
+
+  double epsilon_one = force->numeric(arg[2]);
+  double sigma_one = force->numeric(arg[3]);
+
+  int count = 0;
+  for (int i = ilo; i <= ihi; i++) {
+    for (int j = MAX(jlo,i); j <= jhi; j++) {
+      epsilon[i][j] = epsilon_one;
+      sigma[i][j] = sigma_one;
+      cut_lj[i][j] = cut_lj_global;
+      setflag[i][j] = 1;
+      count++;
+    }
+  }
+
+  if (count == 0) error->all(FLERR,"Incorrect args for pair coefficients");
+}
+
+/* ----------------------------------------------------------------------
+   init specific to this pair style
+------------------------------------------------------------------------- */
+
+void PairLJCutTIP4PCut::init_style()
+{
+  if (atom->tag_enable == 0)
+    error->all(FLERR,"Pair style lj/cut/coul/cut/tip4p requires atom IDs");
+  if (!force->newton_pair)
+    error->all(FLERR,
+               "Pair style lj/cut/coul/cut/tip4p requires newton pair on");
+  if (!atom->q_flag)
+    error->all(FLERR,
+               "Pair style lj/cut/coul/cut/tip4p requires atom attribute q");
+  if (force->bond == NULL)
+    error->all(FLERR,"Must use a bond style with TIP4P potential");
+  if (force->angle == NULL)
+    error->all(FLERR,"Must use an angle style with TIP4P potential");
+  
+  neighbor->request(this);
+
+  // set alpha parameter
+
+  double theta = force->angle->equilibrium_angle(typeA);
+  double blen = force->bond->equilibrium_distance(typeB);
+  alpha = qdist / (cos(0.5*theta) * blen);
+}
+
+/* ----------------------------------------------------------------------
+   init for one type pair i,j and corresponding j,i
+------------------------------------------------------------------------- */
+
+double PairLJCutTIP4PCut::init_one(int i, int j)
+{
+  if (setflag[i][j] == 0) {
+    epsilon[i][j] = mix_energy(epsilon[i][i],epsilon[j][j],
+                               sigma[i][i],sigma[j][j]);
+    sigma[i][j] = mix_distance(sigma[i][i],sigma[j][j]);
+    cut_lj[i][j] = mix_distance(cut_lj[i][i],cut_lj[j][j]);
+  }
+
+  // include TIP4P qdist in full cutoff, qdist = 0.0 if not TIP4P
+
+  double cut = MAX(cut_lj[i][j],cut_coul+2.0*qdist);
+  cut_ljsq[i][j] = cut_lj[i][j] * cut_lj[i][j];
+
+  lj1[i][j] = 48.0 * epsilon[i][j] * pow(sigma[i][j],12.0);
+  lj2[i][j] = 24.0 * epsilon[i][j] * pow(sigma[i][j],6.0);
+  lj3[i][j] = 4.0 * epsilon[i][j] * pow(sigma[i][j],12.0);
+  lj4[i][j] = 4.0 * epsilon[i][j] * pow(sigma[i][j],6.0);
+
+  if (offset_flag) {
+    double ratio = sigma[i][j] / cut_lj[i][j];
+    offset[i][j] = 4.0 * epsilon[i][j] * (pow(ratio,12.0) - pow(ratio,6.0));
+  } else offset[i][j] = 0.0;
+  
+  cut_ljsq[j][i] = cut_ljsq[i][j];
+  lj1[j][i] = lj1[i][j];
+  lj2[j][i] = lj2[i][j];
+  lj3[j][i] = lj3[i][j];
+  lj4[j][i] = lj4[i][j];
+  offset[j][i] = offset[i][j];
+  
+  // check that LJ epsilon = 0.0 for water H
+  // set LJ cutoff to 0.0 for any interaction involving water H
+  // so LJ term isn't calculated in compute()
+  
+  if ((i == typeH && epsilon[i][i] != 0.0) ||
+      (j == typeH && epsilon[j][j] != 0.0))
+    error->all(FLERR,"Water H epsilon must be 0.0 for "
+               "pair style lj/cut/coul/long/tip4p");
+  
+  if (i == typeH || j == typeH)
+    cut_ljsq[j][i] = cut_ljsq[i][j] = 0.0;
+  
+  return cut;
+}
+
+/* ----------------------------------------------------------------------
+  proc 0 writes to restart file
+------------------------------------------------------------------------- */
+
+void PairLJCutTIP4PCut::write_restart(FILE *fp)
+{
+  write_restart_settings(fp);
+
+  int i,j;
+  for (i = 1; i <= atom->ntypes; i++) {
+    for (j = i; j <= atom->ntypes; j++) {
+      fwrite(&setflag[i][j],sizeof(int),1,fp);
+      if (setflag[i][j]){
+        fwrite(&epsilon[i][j],sizeof(double),1,fp);
+        fwrite(&sigma[i][j],sizeof(double),1,fp);
+        fwrite(&cut_lj[i][j],sizeof(double),1,fp);
+      }
+    }
+  }
+}
+
+/* ----------------------------------------------------------------------
+  proc 0 reads from restart file, bcasts
+------------------------------------------------------------------------- */
+
+void PairLJCutTIP4PCut::read_restart(FILE *fp)
+{
+  read_restart_settings(fp);
+  allocate();
+
+  int i,j;
+  int me = comm->me;
+  for (i = 1; i <= atom->ntypes; i++) {
+    for (j = i; j <= atom->ntypes; j++) {
+      if (me == 0) fread(&setflag[i][j],sizeof(int),1,fp);
+      MPI_Bcast(&setflag[i][j],1,MPI_INT,0,world);
+      if (setflag[i][j]) {
+        if (me == 0) {
+          fread(&epsilon[i][j],sizeof(double),1,fp);
+          fread(&sigma[i][j],sizeof(double),1,fp);
+          fread(&cut_lj[i][j],sizeof(double),1,fp);
+        }
+        MPI_Bcast(&epsilon[i][j],1,MPI_DOUBLE,0,world);
+        MPI_Bcast(&sigma[i][j],1,MPI_DOUBLE,0,world);
+        MPI_Bcast(&cut_lj[i][j],1,MPI_DOUBLE,0,world);
+      }
+    }
+  }
+}
+
+/* ----------------------------------------------------------------------
+  proc 0 writes to restart file
+------------------------------------------------------------------------- */
+
+void PairLJCutTIP4PCut::write_restart_settings(FILE *fp)
+{
+  fwrite(&typeO,sizeof(int),1,fp);
+  fwrite(&typeH,sizeof(int),1,fp);
+  fwrite(&typeB,sizeof(int),1,fp);
+  fwrite(&typeA,sizeof(int),1,fp);
+  fwrite(&qdist,sizeof(double),1,fp);
+  fwrite(&cut_lj_global,sizeof(double),1,fp);
+  fwrite(&cut_coul,sizeof(double),1,fp);
+  fwrite(&cut_coulsq,sizeof(double),1,fp);
+  fwrite(&cut_coulsqplus,sizeof(double),1,fp);
+}
+
+/* ----------------------------------------------------------------------
+  proc 0 reads from restart file, bcasts
+------------------------------------------------------------------------- */
+
+void PairLJCutTIP4PCut::read_restart_settings(FILE *fp)
+{
+  if (comm->me == 0) {
+    fread(&typeO,sizeof(int),1,fp);
+    fread(&typeH,sizeof(int),1,fp);
+    fread(&typeB,sizeof(int),1,fp);
+    fread(&typeA,sizeof(int),1,fp);
+    fread(&qdist,sizeof(double),1,fp);
+    fread(&cut_lj_global,sizeof(double),1,fp);
+    fread(&cut_coul,sizeof(double),1,fp);
+    fread(&cut_coulsq,sizeof(double),1,fp);
+    fread(&cut_coulsqplus,sizeof(double),1,fp);  
+  }
+
+  MPI_Bcast(&typeO,1,MPI_INT,0,world);
+  MPI_Bcast(&typeH,1,MPI_INT,0,world);
+  MPI_Bcast(&typeB,1,MPI_INT,0,world);
+  MPI_Bcast(&typeA,1,MPI_INT,0,world);
+  MPI_Bcast(&qdist,1,MPI_DOUBLE,0,world);
+  MPI_Bcast(&cut_lj_global,1,MPI_DOUBLE,0,world);
+  MPI_Bcast(&cut_coul,1,MPI_DOUBLE,0,world);
+  MPI_Bcast(&cut_coulsq,1,MPI_DOUBLE,0,world);
+  MPI_Bcast(&cut_coulsqplus,1,MPI_DOUBLE,0,world);
+}
+
+/* ----------------------------------------------------------------------
+  compute position xM of fictitious charge site for O atom and 2 H atoms
+  return it as xM
+------------------------------------------------------------------------- */
+
+void PairLJCutTIP4PCut::compute_newsite(double *xO,  double *xH1,
+                                        double *xH2, double *xM)
+{
+  double delx1 = xH1[0] - xO[0];
+  double dely1 = xH1[1] - xO[1];
+  double delz1 = xH1[2] - xO[2];
+  domain->minimum_image(delx1,dely1,delz1);
+
+  double delx2 = xH2[0] - xO[0];
+  double dely2 = xH2[1] - xO[1];
+  double delz2 = xH2[2] - xO[2];
+  domain->minimum_image(delx2,dely2,delz2);
+
+  xM[0] = xO[0] + alpha * 0.5 * (delx1 + delx2);
+  xM[1] = xO[1] + alpha * 0.5 * (dely1 + dely2);
+  xM[2] = xO[2] + alpha * 0.5 * (delz1 + delz2);
+}
+
+/* ----------------------------------------------------------------------
+   memory usage of hneigh
+------------------------------------------------------------------------- */
+
+double PairLJCutTIP4PCut::memory_usage()
+{
+  double bytes = maxeatom * sizeof(double);
+  bytes += maxvatom*6 * sizeof(double);
+  bytes += 2 * nmax * sizeof(double);
+  return bytes;
+}
diff --git a/src/MOLECULE/pair_lj_cut_tip4p_cut.h b/src/MOLECULE/pair_lj_cut_tip4p_cut.h
new file mode 100644
index 0000000000..5aaacbed78
--- /dev/null
+++ b/src/MOLECULE/pair_lj_cut_tip4p_cut.h
@@ -0,0 +1,66 @@
+/* ----------------------------------------------------------------------
+   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
+   http://lammps.sandia.gov, Sandia National Laboratories
+   Steve Plimpton, sjplimp@sandia.gov
+
+   Copyright (2003) Sandia Corporation.  Under the terms of Contract
+   DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
+   certain rights in this software.  This software is distributed under
+   the GNU General Public License.
+
+   See the README file in the top-level LAMMPS directory.
+------------------------------------------------------------------------- */
+
+#ifdef PAIR_CLASS
+
+PairStyle(lj/cut/tip4p/cut,PairLJCutTIP4PCut)
+
+#else
+
+#ifndef LMP_PAIR_LJ_CUT_TIP4P_CUT_H
+#define LMP_PAIR_LJ_CUT_TIP4P_CUT_H
+
+#include "pair.h"
+
+namespace LAMMPS_NS {
+
+class PairLJCutTIP4PCut : public Pair {
+ public:
+  PairLJCutTIP4PCut(class LAMMPS *);
+  virtual ~PairLJCutTIP4PCut();
+  virtual void compute(int, int);
+  void settings(int, char **);
+  void coeff(int, char **);
+  void init_style();
+  double init_one(int, int);
+  virtual void write_restart_settings(FILE *);
+  virtual void read_restart_settings(FILE *);
+  void write_restart(FILE *);
+  void read_restart(FILE *);
+  double memory_usage();
+
+ protected:
+  double cut_lj_global,cut_coul_global;
+  double cut_coul,cut_coulsq;
+  double cut_coulsqplus;       // extended value for cut_coulsq
+  double **cut_lj,**cut_ljsq;
+  double **epsilon,**sigma;
+  double **lj1,**lj2,**lj3,**lj4,**offset;
+
+  int typeH,typeO;             // atom types of TIP4P water H and O atoms
+  int typeA,typeB;             // angle and bond types of TIP4P water
+  double alpha;                // geometric constraint parameter for TIP4P
+  double qdist;
+
+  int nmax;                    // info on off-oxygen charge sites
+  int **hneigh;                // 0,1 = indices of 2 H associated with O
+                               // 2 = 0 if site loc not yet computed, 1 if yes
+  double **newsite;            // locations of charge sites
+
+  void allocate();
+  void compute_newsite(double *, double *, double *, double *);
+};
+}
+
+#endif
+#endif